Composite plasticizer, silicon nitride green body and preparation method therefor, and silicon nitride ceramic piece

Abstract

A composite plasticizer, comprising a first plasticizer and a second plasticizer. The first plasticizer comprises at least one of a diol polymer and a diol polymer monomethyl ether. The diol polymer is HO-(CaH2aO)b-H. The diol polymer monomethyl ether is HO-(CaH2aO)b-CH3, wherein 2≤a≤6, and a weight-average molecular weight is 2,000-10,000. The second plasticizer has a molecular formula of R1-(CmH2mO)n-R2, wherein 2≤m≤6, 2≤m*n≤30, R1 is one of hydroxyl, alkoxy, or a carboxylate group, and R2 is one of hydrogen, alkyl, or alkyl carbonyl.

Description

Composite plasticizers, silicon nitride green bodies and their preparation methods, silicon nitride ceramic sheets

[0001] This application claims priority to Chinese Patent Application No. 202411182310.X, filed with the Chinese Patent Office on August 26, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of ceramic materials technology, and in particular to a composite plasticizer, silicon nitride green body and its preparation method, and silicon nitride ceramic sheets. Background Technology

[0003] Currently, silicon nitride ceramic sheets are typically produced using the casting process. This involves preparing a slurry from silicon nitride powder, casting it into a green silicon nitride sheet, and then sintering it at high temperature to obtain the finished silicon nitride ceramic sheet. To ensure the mechanical toughness and morphological integrity of the green silicon nitride sheet, plasticizer components, such as dimethyl phthalate, are added to the slurry formulation.

[0004] Dimethyl phthalate (DMT), as the most widely used plasticizer, is extensively applied in industries such as food processing and packaging, flooring manufacturing, and automobile production. However, with increasing reports of harmful incidents involving phthalates to human health and the environment, the use of these substances is beginning to be restricted. Although the sintering process of silicon nitride ceramic sheets reaches temperatures above 1500℃, which can completely decompose DMT, contact with phthalates is still unavoidable during the contact process with silicon nitride cast green bodies and during the debinding and binding processes, thus posing potential environmental and health risks. Technical issues

[0005] The purpose of this application is to provide a composite plasticizer that can replace phthalate plasticizers, ensuring plasticizing effect while reducing environmental and health risks. Technical solutions

[0006] This application provides a composite plasticizer, comprising a first plasticizer and a second plasticizer. The first plasticizer comprises at least one of a glycol polymer and a glycol polymer monomethyl ether; the glycol polymer has the molecular formula HO-(C a H 2a O) b -H, the molecular formula of diol polymer monomethyl ether is HO-(C a H 2a O) b -CH3, 2≤a≤6, and the weight-average molecular weight of the glycol polymer and the glycol polymer monomethyl ether is 2000-10000. The molecular formula of the second plasticizer is R1-(C mH 2m O) n -R2, 2≤m≤6, 2≤m*n≤30, R1 is one of hydroxyl, alkoxy or carboxylic acid ester group, and R2 is one of hydrogen, alkyl or alkyl carbonyl group.

[0007] This application also provides a silicon nitride green blank, the raw material of which includes the composite plasticizer as described above.

[0008] This application also provides a method for preparing a silicon nitride green blank, which is used to prepare the silicon nitride green blank as described above, comprising: mixing the raw materials of the silicon nitride green blank to obtain a silicon nitride slurry; and casting the silicon nitride slurry into a green blank to obtain a silicon nitride green blank.

[0009] This application also provides a silicon nitride ceramic sheet, prepared from the silicon nitride green blank as described above, or prepared by the method for preparing the silicon nitride green blank as described above. Beneficial effects

[0010] The composite plasticizer provided in this application includes a high-molecular-weight first plasticizer and a low-molecular-weight second plasticizer. When the composite plasticizer is applied to silicon nitride slurry, the low-molecular-weight second plasticizer has strong mobility and migration ability, which can inhibit the regular arrangement of binder molecular chains in the silicon nitride slurry and reduce the glass transition temperature. The molecular chains of the high-molecular-weight first plasticizer can entangle with the binder in the silicon nitride slurry, thereby reducing the tendency to crystallize. Furthermore, the high-molecular-weight first plasticizer can interact with the low-molecular-weight second plasticizer to limit the migration tendency of the second plasticizer to the surface of the silicon nitride slurry, reducing the probability of "oiling" defects in the later stage of the blank. The embodiments of this application use a composite plasticizer to replace phthalate plasticizers in related technologies, improving the plasticizing effect while reducing environmental and health risks. Embodiments of the present invention

[0011] In a first aspect, this application provides a composite plasticizer, comprising a first plasticizer and a second plasticizer. The first plasticizer comprises at least one of a glycol polymer and a glycol polymer monomethyl ether; the glycol polymer has the molecular formula HO-(C a H 2a O) b -H, the molecular formula of diol polymer monomethyl ether is HO-(C a H 2a O) b -CH3, 2≤a≤6, and the weight-average molecular weight of the glycol polymer and the glycol polymer monomethyl ether is 2000-10000. The molecular formula of the second plasticizer is R1-(C m H 2m O) n-R2, 2≤m≤6, 2≤m*n≤30, where R1 is one of hydroxyl, alkoxy, or carboxylic acid ester groups, and R2 is one of hydrogen, alkyl, or alkyl carbonyl groups. That is, the composite plasticizer includes a high-molecular-weight first plasticizer and a low-molecular-weight second plasticizer. When the composite plasticizer is applied to silicon nitride slurry, the low-molecular-weight second plasticizer has strong mobility and can inhibit the orderly arrangement of binder molecular chains in the silicon nitride slurry, thus lowering the glass transition temperature. The high-molecular-weight first plasticizer can entangle with the binder in the silicon nitride slurry, thereby reducing the tendency to crystallize. Furthermore, the high-molecular-weight first plasticizer can interact with the low-molecular-weight second plasticizer to limit the migration tendency of the second plasticizer to the surface of the silicon nitride slurry, reducing the probability of "oiling" defects in the later stages of the blank. In this application, the composite plasticizer can replace phthalate plasticizers in related technologies, improving the plasticizing effect while reducing environmental and health risks.

[0012] In the first plasticizer, the value of 'a' ranges from 2 to 6, and in the second plasticizer, the value of 'm' ranges from 2 to 6. When the values ​​of 'a' and 'm' meet the above conditions, the polarity of the first and second plasticizer molecules is moderate, and their solubility in the selected solvent system is good, thus achieving the plasticizing effect.

[0013] In the molecular formulas of the first and second plasticizers, the values ​​of a, b, m, and n are all integers.

[0014] For example, the first plasticizer may be PEG4000 (polyethylene glycol with a weight average molecular weight of 4000), PEG6000 (polyethylene glycol with a weight average molecular weight of 6000), PPG4000 (polypropylene glycol with a weight average molecular weight of 4000), or PPG6000 (polypropylene glycol with a weight average molecular weight of 6000). The second plasticizer may be PEG600 (polyethylene glycol with a weight average molecular weight of 600), triethylene glycol di-n-butyl ester, PEPG6500 (polyethylene propylene glycol with a weight average molecular weight of 6500), or dipropylene glycol di-n-butyl ester.

[0015] It is understood that the above exemplary description is merely to provide examples of the first and second plasticizers and is not intended to limit the scope of the first and second plasticizers in this application. Wherein, weight-average molecular weight (M... w The weighted contribution of molecular weight to the total mass can be calculated using the following formula:

[0016] Where, N i Indicates molecular weight M i The number of molecules; M i 2 The term representing the square of the molecular weight significantly amplifies the contribution of the high molecular weight fraction to the total mass; ∑i N i M i This represents the total mass of the polymer.

[0017] Weight-average molecular weight can be tested by light scattering, gel permeation chromatography, ultracentrifugation sedimentation, or small-angle X-ray diffraction.

[0018] In some embodiments, the mass ratio of the first plasticizer to the second plasticizer is 1:(1-2). The first plasticizer has a higher molecular weight and better heat resistance, migration resistance, and stability, while the second plasticizer has a lower molecular weight and better solubility and plasticizing efficiency. By mixing the two in a certain proportion, their respective advantages can be brought into play, the overall performance can be improved, the plasticizing effect and stability can be balanced, and the defect of "oiling" can be reduced.

[0019] Secondly, embodiments of this application also provide a silicon nitride green blank, the raw materials of which include the composite plasticizer as described above.

[0020] By applying the aforementioned composite plasticizer to silicon nitride green blanks, phthalate plasticizers in conventional technologies can be replaced, reducing environmental and health risks. Since the plasticizer simultaneously comprises a high-molecular-weight first plasticizer and a low-molecular-weight second plasticizer, it possesses excellent comprehensive performance. Specifically, the low-molecular-weight second plasticizer exhibits strong mobility and migration capabilities, inhibiting the orderly arrangement of binder molecular chains in the silicon nitride slurry and lowering the glass transition temperature. The high-molecular-weight first plasticizer's molecular chains can entangle with the binder in the silicon nitride slurry, thereby reducing the tendency for crystallization. Furthermore, the high-molecular-weight first plasticizer can interact with the low-molecular-weight second plasticizer to limit the migration of the second plasticizer to the surface of the silicon nitride slurry, reducing the probability of "oiling" defects in the later stages of the blank production. Therefore, in the embodiments of this application, by employing the aforementioned composite plasticizer, the silicon nitride green blanks reduce environmental and health risks while ensuring plasticizing performance and improving product yield.

[0021] In some embodiments, the raw materials for silicon nitride green compacts include the following components by weight: 40-55 parts silicon nitride powder, 1-4 parts sintering aid, 0.5-3 parts dispersant, 4-8 parts binder, 2.5-10 parts composite plasticizer, 30-40 parts solvent, and 0.2-1 parts defoamer.

[0022] The amount of solvent added is controlled at 30-40 parts, which can make the slurry made from the raw materials have a suitable viscosity, reduce the molding difficulty of silicon nitride green blanks, and also reduce the surface defects caused by solvent evaporation during the subsequent drying process of silicon nitride green blanks.

[0023] In some embodiments, the binder comprises polyvinyl butyral (PVB) of different molecular weights, with a weight-average molecular weight of 50,000-200,000 and a hydroxyl content of 17%-23% by mass. By using polyvinyl butyral of different molecular weights as a binder, the stability of the silicon nitride slurry obtained from the raw materials of the silicon nitride green body can be improved, and the risk of cracking during the debinding process can be reduced.

[0024] It is understood that the adhesive comprising polyvinyl butyral of different molecular weights means that the adhesive comprises at least two polyvinyl butyrals of weight average molecular weight, for example, simultaneously comprising polyvinyl butyrals of weight average molecular weight of 50,000 and weight average molecular weight of 200,000.

[0025] In some embodiments, the solvent comprises ethanol and ethyl acetate in a mass ratio of 4:6 to 7:3. The solvent needs to have sufficient solubility for the binder and composite plasticizer to adjust the viscosity of the slurry. The composite solvent of ethanol and ethyl acetate is environmentally friendly and less expensive than the benzene or ketone solvents used in related technologies. Furthermore, the significant difference in boiling points between ethanol and ethyl acetate allows for gradient evaporation during the manufacturing of silicon nitride green bodies, enabling control of the solvent evaporation rate and reducing or avoiding surface cracking defects in the silicon nitride green body caused by excessively rapid solvent evaporation.

[0026] For example, the mass ratio of ethanol to ethyl acetate can be 4:6, 5:5, 6:4, or 7:3.

[0027] In some embodiments, the silicon nitride powder has an α-phase mass percentage > 90%, a particle size D50 < 1 μm, and a specific surface area of ​​10 m². 2 / g-20m 2 / g. The α phase of silicon nitride powder has a high density at high temperatures. Controlling the mass percentage of the α phase in silicon nitride powder to greater than 90% facilitates the formation of a denser ceramic material, thereby improving the overall density and strength. Controlling the particle size D50 of silicon nitride powder to below 1μm ensures good flowability and dispersibility, resulting in uniform distribution of the silicon nitride powder in the slurry. The specific surface area of ​​silicon nitride powder is 10-20m². 2 / g has abundant surface active sites, which can improve its binding performance with other materials and enhance its overall performance.

[0028] To improve the performance of silicon nitride powder, it must also meet the following conditions: heteroatom (Fe, Al, Ca) content <300 ppm, C atom content <0.1 wt%, and oxygen content <1 wt%. The low content of heteroatoms such as iron (Fe), aluminum (Al), and calcium (Ca) in silicon nitride powder helps reduce the precipitation of impurities and phase transformations during the sintering process of silicon nitride green blanks, minimizing adverse effects on material properties. Furthermore, the low heteroatom content improves the material's electrical insulation and chemical stability. A carbon (C) atom content below 0.1 wt% helps prevent carbon deposition during the sintering process of silicon nitride green blanks, maintaining the purity and uniformity of the material. An oxygen content below 1 wt% reduces oxide formation and promotes densification of the silicon nitride powder, improving its mechanical properties.

[0029] In some embodiments, the sintering aid includes at least one of magnesium oxide and yttrium oxide. Magnesium oxide can form a liquid phase at lower temperatures, promoting the rearrangement and densification of materials in the silicon nitride green blank, reducing the sintering temperature, and thus improving production efficiency. Magnesium oxide also contributes to densification and improves microstructure, and it has excellent high-temperature stability, remaining stable during high-temperature sintering and not easily volatilizing or decomposing. Yttrium oxide can also form a liquid phase during sintering, promoting the rearrangement and densification of materials in the silicon nitride green blank, and improving densification.

[0030] In some embodiments, magnesium oxide and yttrium oxide have a purity >99.5%, a particle size D50 <2 μm, and a heteroatom (Fe, Al, Ca) content <300 ppm; moisture content <0.1 wt%. Similar to silicon nitride powder, the sintering aid has high purity and low impurity content, which can reduce or avoid the precipitation of impurities and phase transformation during the sintering process of silicon nitride green blanks, ensuring performance. Smaller particle size helps it to disperse uniformly in the slurry. Lower moisture content reduces bubbles formed by moisture evaporation during the sintering process of silicon nitride green blanks, reduces defect generation, and can increase sintering speed, improve density, and enhance mechanical properties.

[0031] In some embodiments, the dispersant includes at least one of polyvinylpyrrolidone, triethyl phosphate, and castor oil. The dispersant helps prevent material agglomeration in the slurry system, thereby improving overall uniformity. Polyvinylpyrrolidone, triethyl phosphate, and castor oil all possess excellent dispersing properties. Polyvinylpyrrolidone helps form a dense protective film on the material surface, preventing particle agglomeration and reducing surface tension. Triethyl phosphate exhibits good solubility in organic solvent systems and high thermal stability. Castor oil is natural, environmentally friendly, and has a wide range of applications.

[0032] Thirdly, embodiments of this application also provide a method for preparing a silicon nitride green blank, used to prepare the above-mentioned silicon nitride green blank, comprising:

[0033] The raw materials of silicon nitride green compact are mixed to obtain silicon nitride slurry;

[0034] Silicon nitride slurry is cast into a silicon nitride green blank.

[0035] The raw materials for silicon nitride green blanks include the aforementioned composite plasticizer, which can replace phthalate plasticizers in conventional technologies, reducing environmental and health risks and minimizing the "oiling" defect in silicon nitride green blanks. The specific effects have been described above and will not be repeated here.

[0036] The main equipment required for tape casting is the tape casting machine, which has a simple structure, is easy to operate, and can achieve continuous production with high efficiency. Furthermore, the silicon nitride green blanks produced by tape casting have a uniform texture, enabling the preparation of large-area, ultra-thin silicon nitride green blanks, resulting in high material utilization, reduced waste during production, and cost savings.

[0037] For example, the silicon nitride slurry is cast into a green blank using a casting machine. This includes: vacuum degassing the silicon nitride slurry, pouring it into the casting tank, setting the squeegee height to 1.0mm-1.5mm, the casting speed to 50mm / min-100mm / min, and the drying temperature to 40℃-55℃, resulting in a silicon nitride green blank with a thickness of 0.40mm-0.65mm. Vacuum degassing effectively removes air bubbles and volatiles from the silicon nitride slurry, reducing defects such as cracks and voids caused by air bubbles during subsequent molding. Setting the squeegee height to 1.0mm-1.5mm yields a silicon nitride green blank with a target thickness of 0.40mm-0.65mm. Setting the casting speed to 50mm / min-100mm / min ensures high production efficiency and reduces defects during production. Setting the drying temperature to 40℃-55℃ allows the solvent in the silicon nitride slurry to evaporate, while also avoiding thermal stress or damage caused by excessive temperature.

[0038] It is understood that the conditions for silicon nitride casting are only illustrative examples. When preparing silicon nitride green blanks of other target thicknesses, the conditions such as the scraper height can be adjusted adaptively according to the target thickness.

[0039] In some embodiments, raw materials for a silicon nitride green compact are mixed to obtain a silicon nitride slurry, comprising:

[0040] Silicon nitride powder, dispersant, sintering aid and part of solvent are mixed in proportion to obtain the first slurry;

[0041] The binder, composite plasticizer, defoamer and another portion of solvent are mixed in proportion to obtain the second slurry;

[0042] The first slurry and the second slurry are mixed to obtain a silicon nitride slurry.

[0043] That is, in the process of preparing silicon nitride slurry, the binder, composite plasticizer, defoamer and part of the solvent are first made into a second slurry to form a pre-solvent, so that the binder and composite plasticizer are evenly dispersed in the solvent, avoiding problems such as clumping caused by directly mixing all raw materials, thereby reducing the risk of cracking in the prepared silicon nitride green blank and improving the product yield.

[0044] The mixing conditions for silicon nitride powder, dispersant, sintering aid, and some solvents were set as follows: ball milling the mixed raw materials for 10-24 hours at a temperature of 25℃ and a rotation speed of 200-300 rpm to ensure uniform mixing of all components. Through the rotation and grinding action of the ball mill, the silicon nitride powder, dispersant, sintering aid, and some solvents can be mixed uniformly to form a stable first slurry, and the particle size of each component can be refined during the ball milling process.

[0045] The mixing conditions for the binder, composite plasticizer, defoamer, and another portion of the solvent are as follows: the mixture is stirred at 25°C using a high-speed mixer at a speed of 200-400 rpm for 2-5 hours. Since the binder and composite plasticizer are prone to clumping and core formation during ball milling, they are first mixed with the binder, composite plasticizer, defoamer, and solvent by stirring to ensure uniform dispersion of the binder and composite plasticizer in the solvent, forming a pre-solvent-like second slurry.

[0046] The conditions for adding the second slurry to the first slurry are set as follows: the composite slurry after mixing the first and second slurries is ball-milled at a temperature of 25℃ and a rotation speed of 200-300 rpm for 10-24 hours. Ball milling thoroughly mixes the first and second slurries and refines the particle size, improving dispersion performance. Since the binder and composite plasticizer are pre-mixed with the defoamer and solvent to form a pre-solvent, problems such as clumping and core formation are less likely to occur during ball milling, which helps to achieve uniform dispersion and reduces the risk of cracking in the silicon nitride green body later.

[0047] Fourthly, embodiments of this application also provide a silicon nitride ceramic sheet, prepared from the above-described silicon nitride green blank, or prepared by the above-described method for preparing silicon nitride green blank. The silicon nitride ceramic sheet provided in this application embodiment has all the effects of the above-described silicon nitride green blank or the method for preparing silicon nitride green blank, and will not be repeated here.

[0048] The present application is described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0049] Unless otherwise specified, the parts in the examples and comparative examples are parts by mass.

[0050] Example 1

[0051] The preparation process of the silicon nitride green blank in this embodiment includes:

[0052] (1) 44.5 parts silicon nitride powder, 1.2 parts magnesium oxide, 1.8 parts yttrium oxide, 1 part triethyl phosphate, 12.5 parts ethanol and 5 parts ethyl acetate were ball-milled at 300 rpm for 12 h at 25 °C to obtain the first slurry;

[0053] (2) 7.5 parts of polyvinyl butyral, 3.75 parts of PEG4000 (polyethylene glycol with a weight average molecular weight of 4000), 3.75 parts of PEG600 (polyethylene glycol with a weight average molecular weight of 600), 0.5 parts of BYK-1790 defoamer, 13 parts of ethanol and 5.5 parts of ethyl acetate were stirred at 25°C and 300 rpm for 2 hours in a high-speed mixer to obtain the second slurry.

[0054] (3) Add the second slurry to the first slurry and ball mill at 300 rpm for 12 h at 25°C to obtain silicon nitride slurry;

[0055] (4) After vacuum degassing the silicon nitride slurry, pour it into the casting tank of the casting machine, set the scraper height to 1.5 mm, the casting speed to 100 mm / min, and the drying temperature to 50 °C; to obtain silicon nitride green blank.

[0056] Example 2

[0057] (1) 43 parts silicon nitride powder, 1.5 parts magnesium oxide, 1.5 parts yttrium oxide, 1 part polyvinylpyrrolidone, 12.5 parts ethanol and 7 parts ethyl acetate were ball-milled at 300 rpm for 12 h at 25 °C to obtain the first slurry;

[0058] (2) 7.5 parts of polyvinyl butyral, 2.5 parts of PEG6000 (polyethylene glycol with a weight average molecular weight of 6000), 5 parts of triethylene glycol di-n-butyl ester, 0.5 parts of BYK-1790 defoamer, 9 parts of ethanol and 9 parts of ethyl acetate were stirred at 25°C and 300 rpm for 2 hours in a high-speed mixer to obtain the second slurry.

[0059] (3) Add the second slurry to the first slurry and ball mill at 300 rpm for 12 h at 25°C to obtain silicon nitride slurry;

[0060] (4) After vacuum degassing the silicon nitride slurry, pour it into the casting tank of the casting machine, set the scraper height to 1.5 mm, the casting speed to 100 mm / min, and the drying temperature to 50 °C; to obtain silicon nitride green blank.

[0061] Example 3

[0062] The preparation process of the silicon nitride green blank in this embodiment includes:

[0063] (1) 40 parts silicon nitride powder, 0.5 parts magnesium oxide, 0.5 parts yttrium oxide, 3 parts triethyl phosphate, 15 parts ethanol and 5 parts ethyl acetate were ball-milled at 300 rpm for 12 h at 25 °C to obtain the first slurry;

[0064] (2) Eight parts of polyvinyl butyral, five parts of PPG4000 (polypropylene glycol with a weight average molecular weight of 4000), five parts of PPG500 (polypropylene glycol with a weight average molecular weight of 500), 0.2 parts of BYK-1790 defoamer, 13 parts of ethanol and 4.8 parts of ethyl acetate were stirred at 25°C and 300 rpm for 2 hours in a high-speed mixer to obtain the second slurry.

[0065] (3) Add the second slurry to the first slurry and ball mill at 300 rpm for 12 h at 25°C to obtain silicon nitride slurry;

[0066] (4) After vacuum degassing the silicon nitride slurry, pour it into the casting tank of the casting machine, set the scraper height to 1.0 mm, the casting speed to 75 mm / min, and the drying temperature to 50 °C; to obtain silicon nitride green blank.

[0067] Example 4

[0068] The preparation process of the silicon nitride green blank in this embodiment includes:

[0069] (1) 55 parts silicon nitride powder, 4 parts magnesium oxide, 0.5 parts triethyl phosphate, 12 parts ethanol and 4.5 parts ethyl acetate were ball-milled at 300 rpm for 12 h at 25 °C to obtain the first slurry.

[0070] (2) Four parts of polyvinyl butyral, one part of PPG6000 (polypropylene glycol with a weight average molecular weight of 6000), 1.5 parts of dipropylene glycol di-n-butyl ester, one part of BYK-1790 defoamer, 12 parts of ethanol and 4.5 parts of ethyl acetate were stirred at 25°C and 300 rpm for 2 hours in a high-speed mixer to obtain the second slurry.

[0071] (3) Add the second slurry to the first slurry and ball mill at 300 rpm for 12 h at 25°C to obtain silicon nitride slurry;

[0072] (4) After vacuum degassing the silicon nitride slurry, pour it into the casting tank of the casting machine, set the scraper height to 1.5 mm, the casting speed to 50 mm / min, and the drying temperature to 50 °C; to obtain silicon nitride green blank.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that 3.75 parts of PEG4000 and 3.75 parts of PEG600 in Example 1 are replaced with 7.5 parts of dibutyl phthalate, while the other conditions remain the same as in Example 1.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that 3.75 parts of PEG4000 and 3.75 parts of PEG600 in Example 1 are replaced with 7.5 parts of glycerol, while the other conditions remain the same as in Example 1.

[0077] The viscosity, green body thickness, and dimensional stability of the silicon nitride slurries in Examples 1-4 and Comparative Examples 1-2 were tested. Viscosity testing followed the viscosity test method in GB / T 10247-2008. Thickness testing involved measuring at four random points on the silicon nitride green body and calculating the average value. Dimensional stability testing involved measuring the length, width, and thickness of the silicon nitride green body after preparation, and then retesting these dimensions after 7 days of storage, comparing the results. The test results are shown in Table 1.

[0078] Table 1. Comparison of test results of silicon nitride green blanks in different embodiments and comparative examples.

[0079] Comparing Examples 1-4 with Comparative Example 1 reveals that in Examples 1-4, a composite plasticizer replaced dibutyl phthalate in Comparative Example 1, ensuring a higher viscosity of the slurry, resulting in a thicker silicon nitride green body with excellent dimensional stability and no oil seepage issues. In other words, by using the composite plasticizer provided in this application to replace conventional phthalate plasticizers, the prepared silicon nitride green body maintains excellent performance. The slurry viscosity, silicon nitride green body thickness, dimensional stability, and appearance are comparable to those of Comparative Example 1, which uses phthalate plasticizers. Furthermore, by replacing phthalate plasticizers with composite plasticizers, environmental and safety risks are significantly reduced.

[0080] A comparison of Examples 1-4 and Comparative Example 2 reveals that: because Comparative Example 2 used low molecular weight glycerol as a plasticizer, the viscosity of the slurry was significantly lower than that of Examples 1-4. This resulted in a thinner silicon nitride green blank prepared under the same conditions. Furthermore, the silicon nitride green blank was prone to absorbing water during storage, leading to poor dimensional stability and noticeable warping. In addition, the glycerol in Comparative Example 2 easily migrated to the surface, exhibiting a more pronounced "oiling" phenomenon, resulting in severe adhesion between different silicon nitride green blanks.

[0081] In summary, the embodiments of this application utilize composite plasticizers to replace phthalate plasticizers, resulting in silicon nitride slurry and silicon nitride green bodies exhibiting performance comparable to that achieved using phthalate plasticizers, while also maintaining environmentally friendly characteristics and reducing environmental and health risks. Furthermore, the composite plasticizers provided in these embodiments, compared to low molecular weight plasticizers, ensure the performance of silicon nitride green bodies in multiple ways, producing excellent results.

Claims

1. A composite plasticizer, comprising a first plasticizer and a second plasticizer; in, The first plasticizer comprises at least one of a glycol polymer and a glycol polymer monomethyl ether; the glycol polymer has the molecular formula HO-(C a H 2a O)bH, the molecular formula of the diol polymer monomethyl ether is HO-(C a H2aO) b -CH3, 2≤a≤6, and the weight average molecular weight of the diol polymer and the diol polymer monomethyl ether is 2000-10000; The molecular formula of the second plasticizer is R1-(C m H 2m O) n -R2, 2≤m≤6, 2≤m*n≤30, R1 is one of hydroxyl, alkoxy or carboxylic acid ester group, and R2 is one of hydrogen, alkyl or alkyl carbonyl group.

2. The composite plasticizer according to claim 1, wherein, The mass ratio of the first plasticizer to the second plasticizer is 1:(1-2).

3. The composite plasticizer according to claim 1 or 2, wherein, The first plasticizer includes at least one of polyethylene glycol with a weight average molecular weight of 4000, polyethylene glycol with a weight average molecular weight of 6000, polypropylene glycol with a weight average molecular weight of 4000, and polypropylene glycol with a weight average molecular weight of 6000.

4. The composite plasticizer according to any one of claims 1-3, wherein, The second plasticizer includes at least one of polyethylene glycol with a weight average molecular weight of 600, triethylene glycol di-n-butyl ester, polyethylene propylene glycol with a weight average molecular weight of 6500, and dipropylene glycol di-n-butyl ester.

5. A silicon nitride green, wherein the raw material for the silicon nitride green comprises the composite plasticizer as described in any one of claims 1-4.

6. The silicon nitride green blank according to claim 5, wherein, The raw materials for the silicon nitride green body include the following components by weight: 40-55 parts silicon nitride powder, 1-4 parts sintering aid, 0.5-3 parts dispersant, 4-8 parts binder, 2.5-10 parts composite plasticizer, 30-40 parts solvent and 0.2-1 parts defoamer.

7. The silicon nitride green blank according to claim 6, wherein, The adhesive comprises polyvinyl butyral of varying molecular weights.

8. The silicon nitride green blank according to claim 7, wherein, The polyvinyl butyral has a weight-average molecular weight of 50,000-200,000, and the mass percentage of hydroxyl groups in the polyvinyl butyral is 17%-23%.

9. The silicon nitride green blank according to any one of claims 6-8, wherein, The solvents include ethanol and ethyl acetate.

10. The silicon nitride green blank according to claim 9, wherein, The mass ratio of ethanol to ethyl acetate is 4:6 to 7:

3.

11. The silicon nitride green blank according to any one of claims 6-10, wherein, The silicon nitride powder has an α-phase mass ratio >90%, a particle size D50 of less than 1 μm, and a specific surface area of ​​10 m². 2 / g-20m 2 / g.

12. The silicon nitride green blank according to any one of claims 6-11, wherein, The silicon nitride powder meets the following requirements: heteroatom content <300ppm, carbon atom content <0.1wt%, and oxygen content <1wt%.

13. The silicon nitride green blank according to any one of claims 6-12, wherein, The sintering aid includes at least one of magnesium oxide and yttrium oxide.

14. The silicon nitride green blank according to claim 13, wherein, The magnesium oxide and yttrium oxide meet the following requirements: purity > 99.5%, particle size D50 < 2 μm, heteroatom content < 300 ppm, and moisture content < 0.1 wt%.

15. The silicon nitride green blank according to any one of claims 6-14, wherein, The dispersant includes at least one of polyvinylpyrrolidone, triethyl phosphate, and castor oil.

16. A method for preparing a silicon nitride green blank, used to prepare a silicon nitride green blank as described in any one of claims 5-15, comprising: The raw materials of the silicon nitride green are mixed to obtain silicon nitride slurry; The silicon nitride slurry is cast into a film to obtain the silicon nitride green blank.

17. The method for preparing a silicon nitride green compact according to claim 16, wherein, The process of mixing the raw materials of the silicon nitride green compact to obtain a silicon nitride slurry includes: Silicon nitride powder, dispersant, sintering aid and part of solvent are mixed in proportion to obtain the first slurry; The binder, composite plasticizer, defoamer, and another portion of the solvent are mixed in proportion to obtain a second slurry; The first slurry and the second slurry are mixed to obtain the silicon nitride slurry.

18. A silicon nitride ceramic sheet, prepared from a silicon nitride green blank as described in any one of claims 5-15, or prepared using the method for preparing a silicon nitride green blank as described in claim 16 or 17.

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